Nitration of olefins in the presence of aromatic solvents



United States Patent 2,999,119 NI'IRATION OF OLEFIN S IN THE PRESENCE 0F AROMATIC SOLVENTS Art C. McKinnis, Long Beach, Calif., assignor, by mesne assignments, to Collier Carbon and `Chemical 'Corporation, a corporation of California Filed Dec. 19, 1955, Ser. No. 553,914 9 Claims. (Cl. 260-644) 'I'his invention relates to the nitration of iso-olens with nitrogen tetroxide (N204) to produce predominantly addition products containing two atoms of nitrogen per molecule. of the mixed addition products to produce ultimately a nitroalkane and either an aldehyde or ketone, depending upon the particular olefin employed. It has been found firstly that iso-oleins may be nitrated with N204 under conditions which practically exclude the formation of oxidation products, mono-nitrated products, and nitroso compounds, the product obtained consisting essentially of a mixture of nitro-nitrites, dinitro alkanes, and nitro-nitrates. Secondly it has been found that the mixture of nitro compounds may, without intervening separation or purification, be subjected to hydrolysis and fission in the presence of water and mildly basic catalysts, under certain novel conditions which result ultimately in the sub-Y stantially quantitative iission of each of the nitrated products to produce a mono-ntroalkane and either an aldehyde or a ketone.

The intermediate mixture of nitro compounds is useful as such, or it may be resolved into its components, which are useful as chemical intermediates, solvents, plasticizers, explosives, jet fuels and the like. The over-all process however, is conceived as an economical route to nitromethane and other nitroalkanes. Presently employed methods for producing nitromethane require the hightemperature vapor-phase nitration of methane or other alkane with nitric acid. This process is uneconomical from the standpoint of equipment costs, "corrosion problems, recovery and recycle of unreacted products, and the inherently low yields and conversions obtained. For example, with methane the maximum yields of nitromethane which have been obtained range between about 2go-25%, based on nitric acid. In the present case, the process results in typical yields of nitromethane ranging between about 80-90% of theoretical, based on either N204 or olefin, and yields of aldehyde or ketone ranging betweenv about 60-80%. These results are obtainedmoreover with relatively non-corrosive reactants, simple apparatus, and economical operating conditions, i.e. 10W temperatures and liquid phase.

It is therefore an object of the invention to provide a simple and economical method for producing nitromethane or other nitroalkanes, in high yields from inexpensive raw materials. Anotherpobiect'is to provide` conditions for the liquid phase, low-temperature nitration of olens with N204 which will substantially eliminate side reactions resulting in the formation of nitroso compounds,y alkyl mononitrates,' alkyl mono-nitritcs andvoxidationt products, and will also concomitantly increase the Ayield of those nitrated products which may berlhydrolyzed to form nitroalkanes and valuable carbonyl compounds. A further object is to provide hydrolysisl'conditions best adapted to convert the complex nitration mixture to a nitroalkane and a carbonyl compound, with a minimum of undesirable hydrolytic side-reactions. Other objects will appear hereinafter.

It relates further to the hydrolytic treatment 2,999,119 Patented Sept. V5,V 1961 ICC In the case of isobutene, the over-al1 reactions arev apparently as follows:

It will be observed in each case that the nitrite and? nitrate groups are added to the carbon atom containing the leastjnumber of hydrogenY atoms, and this is the;

general case with other olens. Reaction 3-avtakes placer to a very small extent in the absence of added'oxygen,` and more especially under the preferred reaction conditions wherein the contact time is limited to a few seconds;

The nitration step'is'necessarily carried Yout in theV i presence of a liquid solvent. When solvents' are not, employed, the solid reaction' products may plug the re-` actor, and/or inhibit adequate mixing of the reactants, and cause uneven contact. times; The use of ether-type solvents isiknown in the art, and they are generally r'egarded as essential for reasons pointed out hereinafter.` Ether` solvents may also be employed herein, but for reasons which diier from those dictating its use in prior art processes. alicyelic, or aralkyl, ethers and esters, preferably thosel containing from 2 to `6 carbon atoms. Specific examples include `dimethyl ether, diethyl ether, methyl-ethyl ether,

the like. -Substituted aromatic compounds may also be employed, as for example chlorobenzene, dichlorobenzenes, trichlorobe'nzenes, tetrachlorobenzenes,pentachlorobenzene, hexachlorobenzene, as well as the,corresponding bromobenzenes and iluoro-benzenes.. Also the halogenated toluenes, xylenes, and the like may'also lbe ein-1,.

ployed, ,as well as the nitrated aromatics including nitrobenzene, nitro-toluenes, nitro-xylenes, and: the polynitrated'jaromatics. Nitro-chloro and nitro-bromo Vben-- zenes, toluenes and xylenes may also be employed. Someof these materials are solids at the Areaction temev perature, and hence it may be necessaryrto employ mixtures ofrsolve'nts in order to obtain a suitable composi- Suitable etherv solvents includel aliphatic, Y

reaction temperatures. When using these aromatic solvents, it has been found that, at short contact times as described herein, the results obtained are substantially equal to those obtained when ether solvents are used. This clearly indicates thatmthe formation of an ether adduct of N204 is not essential to the process. It would appear that the principal-function: of the -ether in prior artprocesses involving longer contact times, is to modify or inhibit the reaction of secondary products such as N202, HNO2, and water, rather than to accelerate the reacton between N204 and olefin. The ter-m inert aromatic solvent is used herein to designate the-'above-I mentioned compounds, and others. similar thereto which are not ethers, and do not form addition compounds with N204, and donor enter into the reaction in any significant manner. 4

The nitration is ordinarily carried out at 25 to +30 C., preferably between about -10 and `-l-15" C., and preferably though not necessarily at atmospheric pressures. Temperatures above the maximum limits result in an undesirable increase in oxidation reactions, while lower temperatures unduly decrease the reaction rate. The nitration is carried out in the liquid phase, but in the case of the lower olens, it may be desirable to employ a liquid-vapor phase system with the N204 and solvent in the liquid. phase, and the olen introduced thereto in the vapor phase. Alternatively, the olefin may be dissolved in the solvent and the resulting solution added to liquid N204, or to a solution of N204 in` thesolvent. Y

: Itis? known that olefinsrwill react with N204 in the presencet'o'f ethers`to give Vdinitrogenated addition products; .1 `Early work seems to have resulted in the formatioug mainly-Lof nitrosol compounds, or nitroso-nitrates (-U.S. 'Patent 2,402,315), A principal object in the pres ent easel is to avoid the formation of nitroso compounds since they do not yield the desired products upon alkaline hydrolysis. Later work (U.S. Patent 2,472,550) showsthatt-he. formation of nitroso compounds may be substantially/:reduced by assuring anhydrous conditions during the nitration, and employing a large mole-excess of N204.` Howeven even under these conditions, the total-yieldl-off dinitro, nitro-nitrite, and nitro-nitrate compounds recovered seldom exceeded 65%, based on the olein,-or-80% based on N204, thus indicating that substantial-amounts of other nitrated monomers and/or polymerswere formed, as well as olefin oxidation products;

-It l1as'now been discovered that substantially quantitativeyilds, e.g. 85-95%, of the desired dinitrogenated'. compounds may be obtained, to the practical exclusionV ofoleiin oxidation products and nitroso compounds, E rapidly removing the initially formed nitro compounds froirifcontact with the nitrating agent, in eifect limiting the" contact time of the N204 with the nitrated olens to less than about 2 minutes, preferably less than about 1 minute. Previous methods usually specify a contact time of one to three hours, where the oleiin is added gradually to an excess of N204ether mixture, and the resulting batch is then worked up for recovery of products. It is further found that if the contact time is limited as described, it is unnecessary to assure completely anhydrous conditions. These phenomena indicate apparently that the addition of nitro and nitrite groups proceeds .much more rapidly than does the formation of nitroso groups or nitrate groups. In the case of isobutene it is found that contact times below about 10 seconds at C. are optimum, even when commercial and oxidation products such as alpha-hydroxy-isobutyric acid is substantially nil.

It has been found also that there is no necessity for maintaining either an instantaneous or an over-all moleexcess of nitrating agent, relative to olen. Hence, the liquid N20.,l may be added gradually to an ether solution of the desired olein, or the reverse order of addition may be utilized. From an economics standpoint it may be desirable to employ an over-all excess of olefin, thereby completely utilizing the N204, and avoiding obvious problems connected with its recovery and recycle. The excess olefin may be readily recovered and recycled. In batch processes this may entail passing a relatively small stream of olen through a batch of liquid solvent- N204, and continuing the passage until the N20.,I is substantially completely consumed. In continuous reactors, it may entail adding to a flowing stream of liquid N204- solvent, as for example in a tubular reactor, a first increment of olen, and then adding at least one other increment thereof downstreamwardly, the total olen added being in mole excess.

The mechanism of the numerous reactions which may occur during nitration are so complex and incompletely understood that a detailed theoretical discussion thereof would probably be misleading through over-simplificaton. The process limitations described herein must hence be regarded largely as empirical. However,` it is known that Water will react with nitrogen tetroxide to yield equilibrium proportions of nitric acid, nitrous acid and nitric oxide. It isV believed that all of these materals add to olefns in an undesired manner; nitric acid to yield alkyl mono-nitrates, and nitrous acid to yield alkyl mono-nitrites. Either of the acids may also result n oxidation to e.g. carboxylic acids. Nitric oxide may result in the formation of nitrogen trioxide:

which. may add to oleiins to form nitroso-nitrites or nitro-nitroso compounds. None of these intermediate products yield, upon alkaline hydrolysis, the desired end products. Hence, it would appear that the presence of water in the system is the principal factor which leads to undesired products, unless the precautionary measures outlined herein, e.g. short contact times, areu observed. However, it is not intended to exclude other possible contributing factors. VProlonged contact of nitro-nitrites with excess N204 might be expected to result in oxidation to nitro-nitrates, an elect which is apparently magnified by the addition of oxygen. Long contact times may also favor other relatively slow oxidation reactions.

If itis desired to utilize the nitration mixture as such, or the individual components thereof, this may be accomplished by conventional methods, as by distilling off any excess solvent, olen, Yor N204, and then fractionating the resulting nitro compounds. However, caution is necessary in working up the nitration mixture inasmuch as the nitro-nitrite compounds readily decompose, sometimes explosively. It is therefore ordinarily preferable to treat the nitration mixture with water at lowtempcratures, whereby the nitrite compounds are hydrolyzed to form nitroalkanols wherein the Ahydroxyl group is attached to the carbon atom to which the nitrite group was form- N204 and ethyl ether are employed, which contain significant amounts vof water, e.g. 1-2% by volume in the case of diethylv ether. Under these conditions it is found erly attached. The insoluble residue resultingV from the low temperature hydrolysis is then a stable mixture of nitro-nitrates and dinitro compounds. The aqueous solution contains the nitro alcohol, which may be recovered by extraction with ether or chloroform for example; If the hydrolysis-step is employed, it is preferable to include therein a weak alkali such as calcium carbonate, zinc oxide, calcium hydroxide or the like in order to combine with the liberated nitrous acid formed by hydrolysis. It has been-found that the nitrous acid liberated tends to cause further oxidation of the reaction products.l The solvent may be removed from the nitration product either that the production of nitroso compounds, mononitrates, before or after the hydrolysis.

When the ultimate aim is to produce nitroalkanes, it-

has been found that very substantial improvements in yield are obtained if the nitration mixture is lirst hy' drolyzed at low temperatures, e.g. O-SO" C. for a short period of time, e.g. l-30 minutes, and, then subjected to a more severe hydrolytic iission step wherein the temperature is raised to about 50-150 C. and maintained within that range for about 2-90 minutes or more. It is also found that very benecial results follow when both of the hydrolysis steps are performed in the presence of an alkali, preferably an insoluble or slightly soluble weak alkali. Strong alkalies are disadvantageous because they form water-soluble salts with the acid-form of the nitroalkanes. In the low temperature hydrolysis step, the alkali serves the purpose of combining with any excess N304 remaining from the nitration step, and with the nitrous acid liberated during hydrolysis, thereby avoiding the oxidizing eiiect of nitrous acid. In the high temperature hydrolytic fission step, the alkali, in addition toA combining with the liberated nitrous acid, also appears to act as a catalyst for the hydrolytic fission of dinitro alkanes, nitro-nitrates, and nitro alcohols.

The choice of alkali employed in the hydrolysis steps may hinge upon the type of inorganic nitrite which is ultimately desired. While there is some preference for insoluble alkalies such as calcium carbonate, zinc oxide, magnesium oxide, aluminum hydroxide, etc., other stronger alkalies may be employed if care is exercised to avoid a large instantaneous excess thereof which would be' available for combining with the nitro-alkanes. By obv serving this precaution, bases such as potassium hydroxide, sodium hydroxide, ammonium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, ammo,- nium carbonate, potassium carbonate, potassium bicarbonate, trisodium phosphate, disodium phosphate, sodium acetate, sodium citrate and the like may also be employed. These materials may be added gradually in proportions suliicient to maintain continuously during the hydrolysis reactions a pH between about 4 and 10preferably between about 5 and 9. In the case of the insoluble alkaline materials such as zinc oxide a stoichiometric excess may be employed and the desired pH range is automatically maintained.

The reactions which occur during hydrolysis and fission are not fully understood, but the more important reactions, as exemplified with the isobutene nitration products, are believed to be as follows:

HNO A C a i H2O CHQNO; A

G Ha

l alk. Ha Hs It has not been determined exactly which of the above" individual reactions take place during the low temperature hydrolysis, and which ytake place during the hightemlA perature fission. It Ydoes appear however ythat the initialV hydrolysis of nitrotert butyl nitrite in Equation 2-b occurs exclusively and rapidly during the low temperature hydrolysis, while the iinal fission of the intermediates to form nitromethane and acetone takesvplace predominantly. or exclusively during the high temperature treatment. It has been observed moreover that lower yieldssof nitrof` methane are obtained when the nitration mixture is trans. ferred directly to the boiling hydrolytic medium, withoutv the intervening low temperature hydrolysis. It would appear therefore that `it is preferable to Yeliminate the Vor-H ganic nitrite groups prior to the high temperature s'sion, probably avoiding thereby the oxidative etfectsrof a sudden large excess of nitrous acid, which would be liberated so rapidly at high temperatures as to cause serious oxidation before it could be neutralized by the alkali. This seems especially likely Where insoluble alkalis such as zinc oxide are employed'. It is also possible that the terminal fission reactions are best carried out in the absence of active nitrite groups which might alter the course of reaction. However, in view of the great complexity of possible reactions, it is evident thatl other explanations may be more accurate.

The actual practice of the invention may perhaps'be best understood by reference to the accompanying drawing which is a liowsheet illustrating a particular method for the nitration of isobutene to obtain ultimately nitrof methane and acetone. The isobutene, either in vapor phase, liquid phase, or in solution, is admitted to the` nitration step 1 through line 2. Liquid nitrogen tetroxide is brought in through line 3 andl admixed with solvent. in line 4,. both of which are then brought into the nitra-` tion step. The proportion of nitrogen tetroxide .toV sol# vent may suitably, though not necessarily, range between about 0.5 and 5 moles thereof per mole ofN2O4. The proportion of isobutene may range'eIg. betweenY aboutl 0.6 and 1.5 moles per mole of` N204. In. theinterest of simplicity and to avoid thehandling of excessive vol-. umes, the three materials admitted to the -nitration step may be in roughly equal molar proportions, i.e. l:1:l. 'l'.he nitration is conducted as previously described, either` batch-wise in a suitable tank, or continuously in a tubular; reactor. The temperature of nitration should be con'-V trolled as indicated, preferably between about -'l0' and' via line 5 to the `low temperature hydrolysis step indiy cated at 6, wherein hydrolysis in the presence of water and an alkali is conducted at exg. 0 to 50 C. for about l to 30 minutes. The proportion of water employed is not critical, -but there is usually no necessity for employing more than the volume of nitration mixture. The

pH of the hydrolysis mixture should Vbe mantainedbetween about 4 and yl0, either by Vlimiting the instantaneous proportion of strong alkali, or by employingv a weak Ibase. 'Ihe totaly proportion of alkaliA employed should be at least stoichiometrically AsulilcientY toy rieutralize half of the total organic nitro, nitrite and nitrate` groups, as Well as any excess unreacted nitrogen tetroxide. v

The lowtem-perature hydrolysis mixture is thentransferred via line 7, to the high temperature hydrolyticisf sion step 8, wherein hydrolysis under similar conditions of alkalinity is continued for another 2 to 90 minutes for example, at about 50-150 C. It is feasible at this point to distill off at least a part of the solvent through line for recycle to nitration step 1. lu case an excess of isobutene was employed, this excess will ordinarily be withdrawn with the solvent in line 10 and recycled. In case strong alkalis are employed in the low temperature hydrolysis step, it may be desirable to add additional alkali via line 9 to the hydrolytic fission stage in order to maintain the desired alkalinity. It is essential however to avoid high alkalinity, especially in the highV temperature hydrolytic ssion stage, inasmuch as the soluble acinitromethane salts formed are very reactive, and produce undesired products.

At the end of the hydroly-tic fission period the reaction mixture is transferred via line K11 to distillation step.12, wherein the products are separated by any desired distillation system. The precise distillation procedure employed lwill depend upon the nature of the solvent employed, but in any event little diculty is usually encountered in obtaining adequate separation. Any remaining solvent is distilled oi through line 13 and recycled to line 4.

If an ether solvent is employed, it is preferred to employ the lower aliphatic members boiling below about 65 C., inasmuch as those materials may either be distilled from the reaction mixture without forming an azeotrope, or in those cases where water azeotropes are formed, such azeotropes contain less than about 4% of water and hence may be recycled directly to the nitration step if Ithe preferred short contact times are employed therein. Dimethyl ether and ethyl-methyl ether for example may be readily recovered Without forming an azeotrope. Methylal likewise does not form an azeotrope. Diethyl ether forms an azeotrope with water, which however contains only 1.3% water. The methylpropyl ether-water azeotrope contains only about 2% of water. Any of these azeotropes may be recycled directly. However, it is not meant to exclude the possibility of dehydrating the ether distillate prior to recycling. This may be accomplished by conventional methods at slightly added expense.

Nitromethane forms an azeotrope with water which boils at 83.6 C. However the components of this azeotrope are immiscible and hence may be readily separated. No azeotrope is formed between acetone and nitromethane and those materials may hence be readily separated, nitromethane boiling at 101 C. and acetone at 56.4 C.

In using aromatic solvents, azeotropes with nitromethane are more often encountered during product separation; however such azeotropes usually are higher boiling than the Water-nitromethane azeotrope, and separation is hence easily elected.

' The residue from the distillation step 12 consists of an aqueous solution of inorganic nitrites and nitrates. The proportion of nitrates is ordinarily small. This mixture may be passed via 'line 15 to an oxidation step 16 wherein the nitn'tes are oxidized, as by means of nitric acid, to obtain nitrates. The nitrates may then be recovered in pure form by evaporation at step 17. The inorganic nitrites or nitrates recovered constitute a valuable by-product fertilizer, or they may be utilized for regenerating nitrogen tetroxide.

Many other tertiary olefns may be utilized in a manner similar Ito that described above. It is preferred to utilizetertiary oleiins, i.e. those mono-olelinic hydrocarbons wherein the double bond is linked to a carbon atom which contains no hydrogen atom; all such olens yield ultimately a nitro-alkane and a ketone. It is further preferred to use olens containing between 4 and 12 carbon atoms. The olens which yield aldehydes generally do not result in as high yields of nitro-alkane, primarily because of the greater diiculty in effecting hyaldehydes.

Suitable olens, together withy their final, re-

action products are illustrated in the following table:

TABLE 1 Reaction products f 2,3dimethyl-2butene 2-methyl-2-butene 2-methyl-l-buteue methylidene cyclohexane 2,4,4-trimethy1 pentene-2 2,3-dimethyl butene1 Z-ethyl butene-l 2,3,3-trimethyl butene-l.

2-isopropenyl benzene acetone, Z-nitropropane.

acetone, ntroethane., Y

methyl-ethyl ketone, nitromethane.

cyclohexanone, nitromethane.

methyl neopentyl ketone, nitromethane.

acetone, nitroneopentane.

methyl isopropyl ketone, nitromethane.

diethyl ketone, nitromethane.

methyl isobutyl ketone, nitrometh ane. acetophenone, nitromethane.

Further to illustrate ,the novel features of the invention, the following examples are cited, which should not however be considered as limiting in scope:

Example Batch nitration A. Ntration.-Seventy ml. (|102 gms.) of redistilled, anhydrous nitrogen tetroxide was added to 400 ml. of anhydrous di'ethyl ether at *20 C. A stream of oxygen was bubbled through lthe solution until it became a light brown (originally dark brown), indicating that all N203 was oxidized to N204. Isobutene4 at the rate of 1.5 s.c.f. (standard cubic feet) per *hour was then added, along with a stream of oxygen at the rate' of 0.5 s.c.f. per hour. The addition of isobutene and oxygen Was continued until -the brown color disappeared, indicating that the N204 was completely consumed. The temperature during. the nitration ranged from 10 to -|-f14 C. The resulting nitrated product is found to consist almost exclusively of nitro-tert-butyl nitrite, 1,2-dinitro isobutane and nitro-tert-butyl nitrate.

B. Hydrolyss.-'I`he nitration mixture from part A was then added with stirring to l liter of water at 27 C.

containing l mole (81 gms.) of zinc oxide. 'I'he slurryv was then heated slowly to 7l-82 C., and maintained in that range for 2. hours while continuously distilling oi product at reduced pressure. Forty-six ml.` of nitromethane (89% yield, based on 0.5'0f original N204) was obtained, and 44 ml. of acetone (54% yield based on 0.5 of original N204).

This example shows Vthat high yields of nitromethane may be obtained in batch scale operation if the reactants are substantially completely anhydrous, and even though there is not an excess of N204 throughout the nitration.

Example II l The procedure of Example I was repeated except that the nitration mixture from part A was added dropwise to the H20-Z110 hydrolysis medium while the latter was maintained continuously at -98 Cl 'Ihe product was removed continuously as -water azeotrope at atmospheric pressure. Fractionation of the product gave 16 ml. of nitromethane (31.5% of theoretical) and 9 ml. of 2- nitroisobutene. Moet of the N204 theoretically convertible to nitromethane was consumed in undesired side-reactions, apparently because fission was not proceded by a low temperature hydrolysis stage.

Example Ill Example l-A was repeated with the nitration temperature controlled at -10-0 C; 'Ihe cold nitration product was then added to a slurry of gms. of calcium carbonate in l liter of distilled water at room temperature. The resulting mixture was then heated gradually over a period of about 25 minutes to 100 C. The original cold nitration mixture was yellow, and changed to buff at 65 C., and to orange at 90 C. The product was then distilled 9 overhead, along with the ether solvent. Fractionation yielded 60 ml. of acetone (77% of theoretical) and 44 ml. of nitromethane (86% of theoretical).

This example shows that calcium carbonate is equally as effective in the hydrolysis step as zinc oxide. Other alkaline materials are found to function similarly, so long as the pH is not allowed to rise into the range where acidnitro salts are formed, or t fall into the range where appreciable amounts of free nitrous acid are present.` For example, in a parallel run employing 1 mole of potassium bicarbonate as the alkali, a 73% yield of nitromethane and a 59% yield of acetone was obtained.

When Examples I and III are repeated, employing undried ether (12% water), the nitromethane and acetone yields are substantially reduced. If au excess of N204 is maintained throughout while using undried ether, somewhat better results are obtained, but not as 'good as when dry reactants and stoichiometric proportions of N204 are employed.

Example 1V.Contnuous nitration A coiled tubular reactor, 2 in inside diameter and l2 ft. in length was constructed Iand immersed in an ice bath. The outlet was led through a condenser -to a flask containing the hydrolysis medium, and equipped with a mechanical stirrer. Liquid diethyl ether was pumped into the inlet of the reactor by means of a constant rate pump. A stream of oxygen plus nitrogen was bubbled through a reservoir or" liquid nitrogen tetroxide at about 0 C., and the total gas stream was' then admitted to the inlet ether line. Liquid isobutene was metered into the inlet line at a point downstreamward from the Ngm-oz-N,

iinlet. In all cases the ice bath was maintained at 0 to Run 4-a. -Anhydrous diethyl ether and redistilled N204 was employed. The ether was pumped in at the rate of about 180 mL/hr., the oxygen and nitrogen iiow rates through the liquid N204 were 1.2 and 0.4 s.c.f. per hour, respectively. Isobutene was added at the rate of 1.2 s'.c.f. (1.5 moles) per hour. The nitration product was continuously passed into the hydrolysis flask containing 80 gms. of zinc oxide in 1 liter of distilled water. The temperature of the hydrolysis flask was maintained at about 23-26 C. throughout the nitration period of one hour. During this period 67 gms. (0.73 mole) of N204 had been passed through the reactor. The liquid residence time in the nitration reactor was about 5 sec., yas determined by timing the passage of a color-indicator therethrough.

At the end of one hour the nitration was interrupted, and the contents of the hydrolysis flask, together with ml. of undecanol to prevent foaming, were heated to boiling and the nal products distilled overhead and fractionated. Substantially all of the ether and unreacted isobutene was recovered, and 37 gms. of nitromethane (83% of theoretical) and 33 ml. of acetone (62% of theoretical).

Run 4-b. Run 4-11 is repeated employing commercial N204 and the water azeotrope of diethyl ether containing about 1.3% by volume of water. The yield of nitromethane and acetone is the same as' in run 4-a, within experimental error, showing that the deleterious eiects of water are overcome by operating at short contact times. No appreciable decrease in yield is noted with nitration mixtures containing up to 3% by volume of water.

Run 4-c.-The procedure of run 4-a is repeated omitting the use of oxygen. The nitrogen ow rate through the reactor was increased to 1.6 s.c.f. per hour. Again the yield of nitromethane is greater than 80% and of acetone about 65%, based on N204, showing that oxygen is not necessary at short contact times.

Run 4-d. -The procedure of run 4a is repeated with an oxygen flow rate of 0.6 s.c.f. per hour and a nitrogen iiowv` rate of 0.2 s.c.f. per hour; whereby the residence time inthe reactor isv approximately doubled (10 sec). The yield of nitromethane is about 65% and of acetone about 45%, showing that the V5 sec. contact time is preferable 'to 10 sec. Y

Run 4-e.-Run 4-a lis repeated, but the nitration product is passed directly `into a boiling C.) 4zinc oxide hydrolysis mix-ture.Y The nitromethane yield is reduced to about 45%. I

Rua Y4-J. Run 4 -a was Vrepeated employingin place of the ether solvent,'180 ml.v per hour of benzene. The nitration product was continuously passed into a hydrolysis lask containing 100 grams of calcium carbonate inl liter of distilled water, the ask being maintained at about 23-26 C. throughout the nitration period of 1 hour. In

this run, as in run 4-a, 67 grams of N204 were passed' through the reactor, and the residence time therein was about 5 seconds. Y

The contents of the hydrolysis ask were then heated to boiling .to elect ssion and the products were distilled overhead and fractionated. Substantially all of the benzene and unreacted isobu-tene was recovered, as well as 32 ml. of nitromethane (75 yield based on N204) and 32 m1. of acetone (60% yield).

When chlorobenzene, or nitrobenzene Vis substituted for the benzene in run 4-f, Ysubstantially similar results ar obtained. n

' Example V Gaseous propylene is subjected to nitration under conditions similar to those described in Example l-a, with the nitration temperaturebeing maintained at 0 C. The rev sulting nitrated product is then poured into 1 liter of boiling water.

found to contain a large proportion of Z-nitro isopropanol Iand polymer-ized nitro propylene. The nitro alcohol is more resistant to hydrolytic fission than are the nitrotertiary -alkanols By nitrating a stream of propylene continuously as described in Example 4-a, with a l minute liquid residence time, and passing the nitrated product into cold water, a similar yield of totalnitrated products is recovered.

Example Vl slurry was gradually heated with stirring.V Fractionation Y of the distillate resulted in the recovery of 20 grams of nitromethane and 49 grams of methylxneopentyl ketone.

Substantially similar vresults are obtained when other tertiary'olens are employed in Examples I to IV. Similarly, essentially the same results are obtained when other solvents are employed, with the exception that the nal product recovery system must be modified to account for the different boiling points.

Itis contemplated that many changes may be made in the various details of the process. The true scope of the invention should therefore not be considered as limited Y,

to the above description, but is intended to be embraced by the following claims.v

I claim: v Y 1. In the liquid phase nitration of a tertiary monoolefinic hydrocarbon containing between 4 and l2 carbon atoms with nitrogen tetroxide at a temperature between about 25 and +30 C., the improvements which com- Hydrolysis is continued for about l hour.; during which time a 20%.yield of nitro-propylene was distilled overhead. The remtaining-aqueous solution is" prise (1) carrying out the nitration in the presence of an inert aromatic solvent and in the absence of any solvent containing an ether group, and (f2) limiting the contact of nitrogen tetroxide with the initially produced olen nitration products to a period of time between about 0.1 secondY and 2 minutes. Y

2. A process as defined in claim 1 wherein the solvent employed is selected from the group consisting of aromatic hydrocarbons, nitro-substituted aromaticV hydrocarbons and halogen-substituted aromatic hydrocarbons.

3. A process as deiined in claim 1 wherein the nitration mixture contains substantial traces of water and the rcaction products of water with N204, the total amount of water plus its N204 reaction products being equivalent to not more than about .04 volume of water per volume of reaction mixture.

4. In the liquid phase nitration of isobutene with nitrogen tetroxide at a temperature between about 25 and +30 C., the improvements which comprise (1) carrying out the nitration in the presence of an inert aromatic solvent and in the absence of any solvent containing an ether group, and (2) limiting the contact of nitrogen tetroxide with the initially produced olefin nitration products to a period of time between about 0.1 second and 2 minutes.

5. A process as defined in claim 4 wherein the solvent employed is selected from the group consisting'of aromatic hydrocarbons, nitro-substituted aromatic hydrocarbons and halogen-substituted aromatic hydrocarbons.

6. In the liquid phase nitration of a tertiary monoolefnic hydrocarbon containing between 4 and 12 carbon atoms with nitrogen tetroxide at a temperature between about 25 and +30 C., the improvements which comprise (l) carrying out the nitration in the presence of an inert aromatic solvent and in the absence of any solvent containing an ether group, and (2) limiting the contact of nitrogen tetroxide with the initially produced oleiin nitration products to a period of time between about 0.1 second and 2 minutes, said limiting of contact time being effected by (1) ycontinuously admixing said aromatic solvent, nitrogen tetroxide and oleiin, (2)0immediately thereafter passing the resulting mixture through an elongated tubular reactor maintained at a temperature between about 25 and +30 C., (3) adjusting the flow rate of said mixture through said reactor so as to maintain a liquid residence time therein-between about 0.1 -seconfd` and 2 minutes, and (4) immediately thereafter quenching the reactor effluent in Water to terminate the nitration.

7. A process as defined in claim 6 wherein substantially equal mole-ratios of olefin and nitrogen tetroxide are passed through said reactor, whereby said reactor efuent is substantially free of both olefin and nitrogen tetroxide.

8. A process as defined in claim 6 wherein the moleratio of olefin/nitrogen tetroxide passed through said reactor is greater than 1, whereby said reactor eliuent is substantially free of nitrogen tetroxide.

9. A process as defined in claim 6 wherein the solvent employed is selected from the group consisting of aromatic hydrocarbons, nitro-substituted aromatic hydrocarbons and halogen-substituted aromatic hydrocarbons, and wherein said olen is isobutene.

References Cited in the file of this patent UNITED STATES PATENTS 2,382,241 Levy Aug. 14, 1945 2,384,047 Smith et al. Sept. 4, 1945 2,384,048 Smith et al. Sept. 4, 1945 2,425,367 Denton et al. Aug. 12, 1947 2,472,550 Smith et al June 7, 1949 2,621,205 Doumani et al. Dec. 9, 1952 

1. IN THE LIQUID PHASE NITRATION OF A TERTIARY MONOOLEFINIC HYDROCARBON CONTAINING BETWEEN 4 AND 12 CARBON ATOMS WITH NITROGEN TETROXIDE AT A TEMPERATURE BETWEEN ABOUT -25* AND +30*C., THE IMPROVEMENTS WHICH COMPRISE (1) CARRYING OUT THE NITRATION IN THE PRESENCE OF AN INERT AROMATIC SOLVENT AND IN THE ABSENCE OF ANY SOLVENT CONTAINING AN ETHER GROUP, AND (2) LIMITING THE CONTACT OF NITROGEN TETROXIDE WITH THE INITIALLY PRODUCED OLEFIN NITRATION PRODUCTS TO A PERIOD OF TIME BETWEEN ABOUT 0.1 SECOND AND 2 MINUTES. 